Prior to the present invention, as shown by U.S. Pat. No. 3,847,870, Takekoshi and U.S. Pat. No. 3,850,885, Takekoshi et al, assigned to the same assignee as the present invention, an imide-amine exchange reaction is taught for making polyetherimides catalyzed by Group (II-V) basic metals and compounds and metals and compounds derived therefrom. Displacement of organic monomeric amine from the bisimide can be effected under melt conditions with organic diamine.
Although amine interchange is a valuable route to the manufacture of polyimides, as shown by Takekoshi et al U.S. Pat. No. 3,850,885, in particular situations it is often desirable to salvage bisimide values from polyimide samples in the form of chips or reground granules to use such salvage values in the further production of polyimides. It would be desirable, for example, to be able to salvage bisimide values from scrap polyimide in the form of N-alkyl substituted bisimide which can be readily converted to the corresponding organic dianhydride as shown, for example, by Markezich et al U.S. Pat. No. 4,128,574, assigned to the same assignee as the present invention, based on an imide-anhydride exchange reaction.